Developmental and Structural Section
Villarreal, Juan Carlos , Schuette, Scott , Witters, Jeffrey , Renzaglia, Karen S. , Taylor, Wilson A. .
Comparative morphological and ultrastructural survey of hornwort spores.
Hornworts are one of the most basal groups of land plants and comprise ca. 200 species circumscribed into five to twelve genera. Delimitation of hornwort genera has relied heavily on spore color and external morphology. However, recent studies indicate that superficial spore characteristics do not segregate traditional hornwort genera. In order to evaluate the taxonomic information in hornwort spores, we conducted a survey of spore ornamentation and ultrastructure using light, scanning and transmission electron microscopy. Representative species were sampled from the following genera: Leiosporoceros, Anthoceros, Folioceros, Phaeoceros, Notothylas, Dendroceros, Megaceros, Nothoceros and “Phaeomegaceros” (an unofficial generic segregate of Phaeoceros that shows genetic and morphological affinity with Megaceros ). Spore color is not a consistent feature in hornwort genera. In general, the thickness in spore wall is correlated with spore color, progressing from thin-walled green spores to yellow to thick-walled brown spores. Ornamentations range from smooth in the isobilateral tetrads of Leiosporoceros , vermiculate in some Notothylas and “Phaeomegaceros”, spinose in Anthoceros and Phaeoceros , and tuberculate in Megaceros, Dendroceros and some species of Notothylas . Spore wall ultrastructure ranges from three or four-layered in most taxa to seven layered in Phaeoceros . Globular sporopollenin deposition is diagnostic of Anthoceros spores, while Dendroceros spores produce highly convoluted exines that stretch as the spores become multicellular. Our data provide evidence of homoplasy in spore morphology and ultrastructure, and invite a more comprehensive evaluation of the utility of spore characters in taxonomy and phylogenetics of hornworts.
1 - University of Wisconsin-Eau Claire, Department of Biology, 105 Garfield Ave., P.O. Box 4004, Eau Claire, Wisconsin, 54702-4004, USA
2 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Presentation Type: Poster
Location: Special Event Center (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 12:30 PM